1. Field of the Invention
The present invention relates to vehicle controllers, and more particularly, to vehicle controllers provided with a continuously variable transmission and a motor-generator.
2. Description of the Related Art
Vehicles engines are generally provided with an alternator to generate electric power and a starting motor to start the engine. A motor-generator that combines the functions of both an alternator and a starting motor has recently been proposed for engines. The motor-generator basically includes a rotary shaft, a rotor core, and a stator core. The rotary shaft rotates integrally with a crankshaft, which is rotated by the engine. The rotor is provided on the rotary shaft. A wire is wound about the rotor. The stator core is fixed to an engine body. A stator wire is wound about the stator core to constitute an inductor. A voltage having a predetermined frequency is applied to the motor-generator's stator wire to produce a rotary magnetic field, the frequency of which is advanced with respect to the rotating speed of the rotary shaft. This causes the motor-generator to function as a motor. The rotational drive force of the motor applies a force to start the engine. When the vehicle is traveling, the motor adds accelerating force to the engine.
The motor-generator also functions as a generator when a rotary magnetic field having a frequency delayed with respect to the rotating speed of the rotary shaft is applied. In such a state, the motor-generator produces electric power. Proposals have been made to enhance the engine torque and to improve fuel consumption by motor-generators.
For example, Japanese Unexamined Utility Model 2-3101 describes a vehicle provided with a motor-generator and a continuously variable transmission. The publication proposes methods to improve the energy balance of the engine, upgrade fuel consumption, and enhance engine maneuverability that includes factors such as the acceleration and deceleration ability. In this publication, the motor-generator functions as a generator in correspondence with an engine brake. This decreases the engine speed by applying torque to the engine. However, the motor function of the motor-generator is not effectively used to compensate the engine speed.
The continuously variable transmission has a continuous shifting characteristic and is thus optimum for the purpose of improving maneuverability. However, the continuously variable transmission has a few characteristic problems such as torque fluctuation caused by the moment of inertia that is applied to an input shaft of the transmission. Thus, the combination of the continuously variable transmission and the motor-generator may result in deficiencies.